Method and apparatus for treating mixed waste by pyrolysis

ABSTRACT

A method and apparatus for treating mixed waste by pyrolysis. Organic mass is carbonized by heating to carbon in a pyrolysis reactor ( 3 ) in an oxygen-free environment. Pyrolysis gases are distilled for oil and the gases are used for energy production. Solid matter resulting from pyrolysis is sieved for separating inorganic coarse particles from a carbon fraction. The carbon fraction is milled in two operations, first with a roller mill ( 8 ) and then with a jet mill ( 10 ), a removal of metal being performed between the operations. The pulverized carbon fraction is classified by means of ionizing particle separators (11, 12, 13). The multi-stage particle separation is followed by discharging clean air and recovering fine carbon.

The invention relates to a method for treating mixed waste by pyrolysis,said method comprising carbonizing organic mass by heating in apyrolysis reactor in an oxygen-free environment to carbon, distillingpyrolysis gases for oil and using the gases for energy production,screening solid matter produced in pyrolysis for separating inorganiccoarse particles from a carbon fraction, and milling and classifying thecarbon fraction.

The invention relates also to an apparatus for treating mixed waste bypyrolysis, said apparatus comprising a feed conveyor for mixed waste, adewaterer, a reusable magazine carriage, a pyrolysis reactor, which issupplied with mixed waste by the conveyor and in which organic mass isheatable in an oxygen-free environment to carbon, an oil distillationcolumn for distilling pyrolysis gases for oil while cleaning the gas, asieve for screening solid matter resulting from the pyrolysis reactorfor a fraction containing primarily carbon, and milling equipment formilling the carbon fraction, as well as a classifier and air cleaner forseparating and recovering pure carbon.

Patent publication U.S. Pat. No. 6,244,198 discloses a method andapparatus for the pyrolytic treatment of organic material. This priorknown apparatus can be used also in the present invention as a pyrolysisreactor. Waste disposal methods and equipment, based on pyrolysis, areknown in large numbers, notable examples including Patent publicationsU.S. Pat. No. 5,725,738 and EP-0905213. However, these prior art methodsand equipment do not provide a sufficient solution for theafter-treatment and grading of carbon produced in pyrolysis. However,this would be of paramount importance in terms of using recovered carbonand recycling the same for reutilization. Another unsolved problem withprior art pyrolysis reactors is the fact that the dewatering of waste tobe fed into a pyrolysis reactor and the purification of water recoveredtherefrom have not been worked out with sufficient efficiency. Themethod and apparatus known from International Patent application WO01/04235 are provided with preheating and dewatering of wastes, butthere is no proposal for purification of water recovered therefrom.

It is an object of the invention to provide a method and apparatus forsubstantially enhancing and improving the after-treatment andclassification of recovered carbon, also in view of reutilization.

This object is achieved in the invention by a method as set forth inclaim 1 and by an apparatus as set forth in claim 4. Preferredembodiments of the invention, especially the effective cleaning of waterrecovered from the dewatering of waste, are dealt with in the dependentclaims.

The invention will now be described in more detail by way of examplewith reference to the accompanying drawing, which shows a general blockdiagram for a method and apparatus of the invention, visualizing variousoperations of a treatment process and equipment used therein.

Mixed waste is carried, e.g. from a pile of landfill, on a conveyor 1into a magazine carriage 17, and thence on to a pyrolysis reactor 3. Thereactor 3 may vary in many ways in terms of its design and operation. Asone example, reference can be made to Patent publication U.S. Pat. No.6,244,198. The reactor 3 has a first section 3.1 for heating the mass, asecond section 3.2 for actual pyrolysis, and a third section 3.3 forcooling. Since the reactor 3 can be located far away from a waste dump,the delivery of wastes is performed by a mesh-covered magazine carriage17 from the waste dump to a reactor 3 and further through the reactor 3.Regardless of design and operating mode, a common feature for allreactors 3 is the capability of heating organic mass to carbon in anoxygen-free environment. This carbonization by pyrolysis provides for acontinuous generation of gas, which is delivered to an oil distillationcolumn 4. The oil is recovered and the remaining gas is used for energyproduction, e.g. in a gas turbine and generator 5.

The solid matter resulting from pyrolysis is screened, e.g. with arotary drum sieve 7, for separating inorganic coarse particles from acarbon fraction. The carbon fraction is milled or pulverized with aroller mill 8, and then with a jet mill 10, wherein the milling is basedon colliding air-carbon jets. The milling operations are intervened bythe removal of metals with a separator 9.

The milled or pulverized carbon fraction is classified by means ofionizing particle separators 11, 12, 13. These are used to perform amulti-stage particle separation, primarily for separating metal andmineral particles from carbon. The ionizing particle separators 11, 12,13 are functionally based on ionizing airborne particles flowing througha chamber and collecting the charged particles by means of an electricfield on live collector surfaces (e.g. chamber walls), the particlesbeing recovered therefrom mechanically (e.g. with a vibrator) in acollector tray. What is essential is that sequential ionizing particleseparators constitute a classifier, enabling a separate collection ofmetals and minerals and a recovery of fine carbon from the finalseparator, which has a degree of purity sufficiently high for theproduction of e.g. activated carbon. Thus, the activated carbon,resulting from a separate activated-carbon production process, can beused in a filter 16 for the ultimate cleaning of water recovered fromthe process, especially from the waste dewatering process. Theimpurities accumulated in carbon are removed and carbon is regeneratedby feeding it through a dewatering operation back to the pyrolysisprocess. Clean air is delivered by the final separator 13 in the ionparticle classifier.

In conjunction with the conveyor 1 lies a dewatering unit 2, the waterobtained therefrom being carried through an iron-electrode fittedelectrolytic cell 14. There may be more than one cells connected inparallel. The water, which has been treated electrolytically in the cell14, and the flock, which consists of precipitate, are delivered to aflock separator 15 for separating flock from water, which latter, ifdesired, can be cleaned with an activated carbon filter 16 for servicewater. The water is sufficiently clean for returning to nature as soonas it has passed the flock separator 15. The purification achieved by acombination of the electrolytic cell 14 and the flock separator 15through electroflotation has been described in more detail in theApplicant's Patent publications U.S. Pat. No. 5,888,359 and U.S. Pat.No. 6,086,732. The dewatering unit 2 may be operationally based e.g. onhot air injection for evaporating the water into an air flow, afterwhich the water is condensed from the air. Thermal energy required forhot air injection can be produced by means of hot gases resulting frompyrolysis. The dewatering and water purification process is a completelyclosed process when dealing with a hazardous waste, which may containe.g. prions.

The invention is capable of providing a zero emission pyrolysis forconverting health-hazardous wastes to energy and reusable commodities.

1. A method for treating mixed waste by pyrolysis, said methodcomprising carbonizing organic mass by heating in a pyrolysis reactor(3) in an oxygen-free environment to carbon, distilling pyrolysis gasesfor oil and using the gases for energy production, screening solidmatter produced in pyrolysis for separating inorganic coarse particlesfrom a carbon fraction, and milling and classifying the carbon fraction,wherein the a) milling is performed in two operations, first with aroller mill (8) and then with a jet mill (10), and a removal of metal isperformed between the milling operations; and b) the milled carbonfraction is classified according to particle size/weight by means ofionizing particle separators for effecting a multi-stage particleseparation, which is followed by discharging clean air and recoveringpure carbon.
 2. A method as set forth in claim 1, wherein waste isdewatered prior to pyrolysis and the water emanating from a dewateringunit (2) is cleaned with electroflotation, in which the water is guidedthrough an iron-electrode fitted cell (14), and the resulting flock isthen separated from water.
 3. A method as set forth in claim 2, whereinthe water purified with electroflotation is guided through an activatedcarbon filter (16) and activated carbon for the filter (16) is preparedfrom the end product of a method for treating mixed waste by pyrolysis,which comprises carbonizing organic mass by heating in a pyrolysisreactor (3) in an oxygen-free environment to carbon, distillingpyrolysis gases for oil and using the gases for energy production,screening solid matter produced in pyrolysis for separating inorganiccoarse particles from a carbon fraction, and milling and classifying thecarbon fraction, wherein the a) milling is performed in two operations,first with a roller mill (8) and then with a jet mill (10), and aremoval of metal is performed between the milling operations; and b) themilled carbon fraction is classified according to particle size/weightby means of ionizing particle separators for effecting a multi-stageparticle separation, which is followed by discharging clean air andrecovering pure carbon as said end product; and that the carbon used asa filter is returned to the pyrolysis process for cleaning.
 4. Anapparatus for treating mixed waste by pyrolysis, said apparatuscomprising a conveyor (1) for mixed waste, a dewaterer (2), a magazinecarriage (17), a pyrolysis reactor (3), which is supplied with mixedwaste by the conveyor (3) and in which organic mass is heatable in alimited amount of oxygen to carbon, an oil distillation column (4) fordistilling pyrolysis gases for oil and for cleaning the gas, a sieve (7)for screening solid matter resulting from the pyrolysis reactor (3) fora fraction containing primarily carbon, and milling equipment (8, 10)for milling the carbon fraction, wherein the milling equipment includesa roller mill (8) and a jet mill (10), and that from the jet mill (10)the carbon dust is guided through ionizing particle separators (11, 12,13) for separating air to be discharged from fine carbon to berecovered.
 5. An apparatus as set forth in claim 4, wherein thesequential ionizing particle separators (11, 12, 13) constitute aclassifier for separating particles on the basis of specific gravity,weight and/or size.
 6. An apparatus as set forth in claim 5, wherein theconveyor (1) is provided with a dewatering unit (2), from which water isguided through an iron-electrode fitted electrolytic cell (14) to aflock separator (15) for separating flock from water.
 7. An apparatus asset forth in claim 6, wherein from the flock separator (15), water isguided through an activated carbon filter (16), and activated carbon forthe filter (16) is made from the carbon which is recovered from aclassifier constituted by a plurality of ionizing particle separators(11, 12, 13).
 8. An apparatus as set forth in claim 4, wherein theconveyor (1) is provided with a dewatering unit (2), from which water isguided through an iron-electrode fitted electrolytic cell (14) to aflock separator (15) for separating flock from water.
 9. An apparatus asset forth in claim 8, wherein from the flock separator (15), water isguided through an activated carbon filter (16), and activated carbon forthe filter (16) is made from the carbon which is recovered from aclassifier constituted by a plurality of ionizing particle separators(11, 12, 13).
 10. An apparatus as set forth in claim 5, wherein from theflock separator (15), water is guided through an activated carbon filter(16), and activated carbon for the filter (16) is made from the carbonwhich is recovered from a classifier constituted by a plurality ofionizing particle separators (11, 12, 13).